The Invention pertains to a method for controlled production of particle-shaped material from the molten substance.
Production of particle-shaped material from molten substance is known for plastic, natural substances, glasses and even metals. There is a constantly increasing demand for powders of such types of materials having small grain size.
These known methods produce a particle-shaped material which can also be referred to as powder, granulate, smalls or something similar. For the sake of simplicity, these particle-shaped materials are referred to below as powder. These kinds of powders are used for example in injection moulding techniques, production of alloys, sintering techniques, bonding materials, catalysts, paints and lacquers, cellular plastic production etc. The market for these applications has a high demand of powder having small. grain size of certain particle shapes in large quantities at low cost. Till now these types of powders were produced a.o., in that—as described for example in the document WO 01/62987, fluid fused substances like oxidic slag, glasses or fused metal are nozzle jetted or atomised in some other way in a chamber by high pressure gas expansion—for example, with the help of rotating plates/discs which centrifuge away the generated droplets and thus pulverise (Rotating Disc Method) , or even by means of Roller Atomisation—whereby molten metal droplets meet an rotating rollers and are centrifuged away from them and get solidified an the flight path. Another typical method is water atomisation. To a large extent however, mainly gas atomisation is used. For this, nozzles, like Laval-nozzles are used, in which the fluid molten substance is first strongly accelerated and thereafter sporadically expanded under strong acceleration to a high velocity at the nozzle exit into a chamber and thus atomised.
A typical method is described in the Austrian patent document 2987350 of Eckart-Werke. Ideally, the molten substance is further distributed by gas currents simultaneously along with this sporadic expansion at the nozzle outlet and thus finely distributed fused droplets are obtained which get solidified an cooling and thus form the powder. Hence the known generic method consists of bringing a material melt after exit out of the nozzle in contact with gas and simultaneously sporadically expanding it. This known method is disadvantageous to the extent that it was very difficult to control, had to be interrupted very frequently and could not be carried out continuously. Finally, the energy costs were also very high.
From the document WO 99/11407 of Pacific Metals Co. Ltd. it is known that one can obtain metallic powder through atomisation of fused-fluid metal, in that an away current of the fused-fluid metal is atomised at the exit of a nozzle by introducing it into the centre of the nozzle along with a laminar-gas current enveloping it and by introducing a fluid current an an exit of both the currents from a conical nozzle, which strengthen the atomisation. In this case, in addition to the gas current a fluid current should also be provided, which is complicated.
From the document EP-A-1038976 a method is known, in which sprayed molten droplets in the inner region of a spray jet are heated up once again in the inner region of a cooled cooling chamber by means of post-combustion of hot gases after exit from the spray nozzle and thus a better distribution of the molten droplets is achieved by means of the heated combusting gases and hence the fineness of the produced powder is improved. This method is very energy intensive, as it requires cooling of the walls of the cooling chamber and also cumbersome measures will have to be carried out for producing small particle sizes.
A disadvantage of the known method is also, that these did not try to control the particle size or shape; a uniform particle size spectrum was generated by setting the gas/fluid-ratio, on which no other influence could be exercised.
It is therefore the task of this invention to create a continuous, efficient method for controlled production of powders from material melts, which would allow control of size and shape of the produced particles.